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Positive earnings news from the likes of Facebook, Google and Apple helped boost tech shares in what was otherwise a gloomy week for the markets.

The Dow Jones Industrial Average, Standard and Poor's 500 index and the Nasdaq stock exchange closed down Friday. The slide made January the worst month for Wall Street since May 2012.

Concerns about slowing growth in China and emerging markets around the world depressed share prices this month. But on Friday, some bellwether tech stocks managed to make gains, as the Nasdaq computer index rose 16.01 points to close at 2,007.95.

One disappointment: earnings per share, at $12.01, was under analyst estimates of $12.26.

On the whole, analysts applauded the results, and were happy with the company's announcement earlier in the week that it was selling its Motorola Mobility handset unit to Lenovo. Even thought Google bought the company in 2012 for more than $12 billion and is now selling it for $2.91 billion, it is getting rid of a business that was not contributing to profit.

Motorola handsets also put Google in competition with manufacturers that are using -- or may use -- the Google-developed Android OS. Google is keeping Motorola-related patents, so it is retaining important intellectual property.

"In addition to the strong top line, sentiment appears bolstered by the announced sale of the MMI handset business to Lenovo, which should help restore higher revenue growth and margins at the corporate level," according to Canaccord Genuity analyst Michael Graham in a research note. "We are slightly raising estimates and continue to believe Google is a healthy core Internet and Tech holding," Graham said.

Yahoo's report on Alibaba, the Chinese Internet giant in which it has a stake, was worrying. Yahoo said that Alibaba's revenue for the quarter ending in September was $1.78 billion, up 51 percent year over year. For most companies, that would sound good. But for Alibaba, that means sales growth is slowing. In the prior three month period, growth was up 61 percent year over year, and for the quarter before that, growth was up 71 percent year over year.

Nevertheless, in a strong day for tech on the markets, Yahoo shares closed Friday at $36.01, up by $0.70.

Amazon shares, on the other hand, plunged even though it turned in a strong quarter. Amazon shares went into free-fall Friday, sinking $44.32 to close at $358.69.

Its strong results didn't quite come up to expectations. The company said that for the fourth quarter it had a profit of $239 million, or $0.51 cents a share, up from 97 million, or $0.21 cents a share, a year earlier. But estimates from analysts polled by Thomson Reuters were for $0.66.